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Abstract:

A method is provided in a receiving node for handling status information
of data units transmitted from a sending node to the receiving node over
a radio link. The receiving node establishes (401) that a number of data
units that has been transmitted by the sending node are missing. The
receiving node sends (402) a reduced status message to the sending node
over the radio link, which message is reduced such that it comprises the
negative acknowledgement for a first part of missing data units and omits
negative acknowledgements for the rest of the missing data units. The
omitted negative acknowledgement for the rest of the missing data units
will not erroneously be interpreted as correctly received data units by
the sending node.

Claims:

1. A method in a receiving node for handling status information of data
units transmitted from a sending node to the receiving node over a radio
link, each data unit having a respective sequence number, the method
comprising: determining that a number of data units transmitted by the
sending node are missing at the receiving node; and generating a reduced
status message comprising negative acknowledgments for a first part of
the missing data units and omitting negative acknowledgments for the rest
of the missing data units; and sending the status message from the
receiving node to the sending node over the radio link.

2. The method according to claim 1, wherein the generating step further
comprising: including the special identifier in a control PDU type, CPT,
field of a status message to indicate that the status message is the
reduced status message.

3. The method according to claim 1, wherein the generating step further
comprises: omitting a field of acknowledgment from the status message to
allow transmission of additional negative acknowledgments.

4. The method according to claim 1, further comprising: generating one or
more second reduced status messages comprising the rest of the missing
data units, wherein the one or more second reduced status messages are
incapable of causing the sending node to advance the transmission window.

5. The method according to claim 1, further comprising: maintaining a
lower window edge corresponding to a sequence number of the oldest
outstanding data unit; and maintaining an upper window edge corresponding
to a sequence number of the highest received data unit.

6. A receiving node for handling status information of data units
transmitted from a sending node to the receiving node over a radio link,
each data unit having a respective sequence number, the receiving node
comprising: an establishing circuit configured to establish that a number
of data units transmitted by the sending node are missing at the
receiving node; and a sending circuit configured to send a reduced status
message from the receiving node to the sending node over the radio link,
wherein the reduced status message comprises negative acknowledgments for
a first part of the missing data units and omitting negative
acknowledgments for the rest of the missing data units.

7. The receiving node according to claim 6, wherein the reduced status
message further comprises the special identifier in a control PDU type,
CPT, field of a status message to indicate that the status message is the
reduced status message.

8. The receiving node according to claim 6, wherein the status message
further lacks a field of acknowledgment from the status message to allow
transmission of additional negative acknowledgments.

9. The receiving node according to claim 6, wherein the sending circuit
is configured to send one or more second reduced status messages
comprising the rest of the missing data units, wherein the one or more
second reduced status messages are incapable of causing the sending node
to advance the transmission window.

10. The receiving node according to claim 6, further comprising a
processor configured to: maintain a lower window edge corresponding to a
sequence number of the oldest outstanding data unit; and maintain an
upper window edge corresponding to a sequence number of the highest
received data unit.

11. A method in a sending node for handling status information of data
units transmitted from the sending node to a receiving node over a radio
link, the method comprising: transmitting a stream of data units over the
radio link to the receiving node, the receiving node correctly receiving
some of the data units but missing a number of data units, each data unit
having a respective sequence number; receiving a status message from the
receiving node over the radio link; and interpreting the status message
as a reduced status message comprising negative acknowledgments for a
first part of the missing data units, and omitted negative
acknowledgments for the rest of the missing data units.

12. The method according to claim 11, further comprising: receiving one
or more second reduced status messages comprising the rest of the missing
data units, wherein the one or more second reduced status messages are
incapable of causing the sending node to advance the transmission window.

13. The method according to claim 11, further comprising: maintaining a
lower window edge corresponding to a sequence number of the oldest
outstanding data unit for which no positive acknowledgment has been
received.

14. The method according to claim 13, further comprising: advancing the
lower window edge up to a next oldest outstanding data unit in response
to receiving the positive acknowledgment for the oldest outstanding data
unit in the status message.

15. The method according to claim 11, further comprising: maintaining an
upper window edge corresponding to a sequence number of the next data
unit to be transmitted.

16. The method according to claim 11, wherein the status message is
interpreted as the reduced status message with reference to a special
identifier included in a control PDU type, CPT, field of the status
message.

17. A sending node for handling status information of data units
transmitted from the sending node to the receiving node over a radio
link, the sending node comprising: a sending circuit configured to
transmit a stream of data units over the radio link to the receiving
node, the receiving node correctly receiving some of the data units but
missing a number of the data units, each data unit having a respective
sequence number; a receiving circuit configured to receive a status
message from the receiving node over the radio link; and a processor
configured to interpret the status message as a reduced status message
comprising negative acknowledgments for a first part of the missing data
units, and omitted negative acknowledgments for the rest of the missing
data units.

18. The sending node according to claim 17, wherein the receiving circuit
is further configured to receive one or more second reduced status
messages comprising the rest of the missing data units, wherein the one
or more second reduced status messages are incapable of causing the
sending node to advance the transmission window.

19. The sending node according to claim 17, wherein the processor is
further configured to maintain a lower window edge corresponding to a
sequence number of the oldest outstanding data unit for which no positive
acknowledgment has been received.

20. The sending node according to claim 19, wherein the processor is
further configured to advance the lower window edge up to a next oldest
outstanding data unit in response to receiving the positive
acknowledgment for the oldest outstanding data unit in the status
message.

21. The sending node according to claim 17, wherein the processor is
further configured to maintain an upper window edge corresponding to a
sequence number of the next data unit to be transmitted.

22. The sending node according to claim 17, wherein the processor is
configured to interpret the status message as the reduced status message
with reference to a special identifier included in a control PDU type,
CPT, field of the status message.

Description:

RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent application Ser.
No. 14/159,711, filed Jan. 21, 2014, which is a continuation of U.S.
patent application Ser. No. 12/866,534, filed Aug. 6, 2010, which claims
priority from International Patent Application No. PCT/SE2008/051047,
filed Sep. 18, 2008, which claims priority from U.S. Provisional Patent
Application No. 61/027,110 filed Feb. 8, 2008, all of which are hereby
incorporated by reference herein in their entirety.

TECHNICAL FIELD

[0002] The present invention basically relates to the general field of
data unit communication comprising a method and an arrangement in a
sending node and a method and an arrangement in a receiving node. In
particular, it relates to handling status information of data units
transmitted from the sending node to the receiving node over a radio
link.

BACKGROUND

[0003] In today's data unit communication, an amount of data is divided
into individual units, and said units are transmitted to a desired
receiver over an appropriate communication path. This form of data
communication is very well known and in wide use. The sending node may
e.g. be a radio base station and the receiving node may be a user
equipment such as a mobile phone, portable computer, Personal Digital
Assistant (PDA) or vice versa. Most of these systems use bi-directional
radio communication where both nodes transmit and receive data units
simultaneously or alternating.

[0004] Such data units carry a variety of names in the context of
different communication systems and communication protocols, such as
packets, frames, segment, protocol data units, etc. The term "data unit"
as used in the present specification and claims generically refers to any
such division of a data amount.

[0005] In order to ensure the complete and correct transmission of data
units from a transmitting to a receiving protocol peer, a mechanism
referred to as ARQ (Automatic Repeat reQuest) is often used. ARQ
mechanisms are commonly part of link layer protocols such as the Radio
Link Control (RLC) protocol or the Medium Access Control (MAC) protocol
specified for the Universal Mobile Telecommunications System (UMTS)
Terrestrial Radio Access Network (UTRAN) as well as for the
Evolved-UTRAN. When using an ARQ mechanism, the receiver of data units
sends feedback messages to the sender, such that the sender can determine
whether sent data units were properly received, and if not, to
appropriately perform retransmissions of data units.

[0006] A feedback message is a control data unit that is typically sent
from the receiving entity of an ARQ protocol to the transmitting peer
entity.

[0007] Feedback messages are often referred to as status message, status
report, status, etc. They may have different formats depending on the
protocol specification. Known implementations of such status messages
comprise one or more references to protocol data units, or parts thereof,
received or expected by the receiving protocol entity. These references
are typically denoted as positive and/or negative acknowledgements and
also referred to as ACK or NACK. An acknowledgement provides the
transmitting protocol entity with information about successful or
unsuccessful reception of one or more data units at the receiving
protocol entity. Many of the known ARQ protocols assign a so-called
sequence number (SN) to each data unit and use this sequence number as
reference in status messages. A positive acknowledgement for the data
unit with a given sequence number may then be referred to as ACK_SN
whereas a negative acknowledgement may be denoted as NACK_SN. Widely,
known protocols use lists and/or bitmaps in status messages. An
acknowledgement may be explicit, i.e., represent the state of one
particular data unit or it may be cumulative, i.e., provide information
about the state of a collection of data units.

[0008] The radio link control protocol specified for E-UTRAN uses
combinations of the two. In said protocol the positive acknowledgement is
cumulative, i.e., it positively acknowledges all data units with a
sequence number up to but not including ACK_SN that are not explicitly
negatively acknowledged. In the status messages of said protocol a
negative acknowledgements is transmitted by means of a NACK_SN field for
each not received data unit below ACK_SN.

[0009] Data units and control data units such as status messages may
comprise a payload section and a header section where the former contains
the actual information to be exchanged between the peer protocol entities
and the latter carries information needed to decode that information
correctly. The header section of a data unit may for example comprise the
associated sequence number.

[0010] One example of a status message is the LTE RLC STATUS PDU in
E-UTRAN disclosed in FIG. 1. In the example of FIG. 1, each row comprises
eight bits, i.e. one octet (Oct 1, Oct 2, etc.). The data unit comprises
a payload section and a header section. The header section comprises a
Data/Control (D/C) and a Control PDU Type (CPT) field. The D/C field
indicates whether the data unit is an RLC data PDU carrying payload from
higher layers or an RLC control PDU, namely a status message. The CPT
field indicates the type of the RLC control PDU. The payload section
following the header section comprises an ACK_SN field and an extension
flag E1. The former carries the sequence number following that of the
highest received data unit and it cumulatively acknowledges all data
units up to but not including that sequence number which are not
negatively acknowledged in the remainder of the status message. The E1
flag indicates whether or not a set of NACK_SN, E1 and E2 follows. The
NACK_SN field comprises the sequence number of a data unit which has been
detected as missing by the receiving protocol entity, i.e., a negative
acknowledgement. The E2 field indicates whether or not a set of SOstart
and SOend follows. The SOstart field together with the SOend field
indicates the portion of the data unit with SN=NACK_SN (the NACK_SN which
the SOstart is related to) that has been detected as lost at the
receiving protocol entity. In this example the ACK_SN field as well as
all NACK_SN fields comprise 10 bit and can therefore address
210=1024 sequence numbers. In order to be able to transmit more data
units, a wrap-around mechanism may be used so that the sequence number
space can be re-used.

[0011] In accordance with the generic description of ARQ mechanisms the
transmitting side of an LTE RLC Acknowledged Mode (AM) RLC entity
interprets a received STATUS PDU so that all Acknowledge Mode Data (AMD)
PDUs up to but excluding the AMD PDU with SN=ACK_SN have been received by
its peer AM RLC entity, excluding those AMD PDUs indicated in the STATUS
PDU with NACK_SN and also excluding portions of AMD PDUs indicated in the
STATUS PDU with NACK_SN, SOstart and SOend.

[0012] In general and also in the particular example of LTE RLC the status
messages provide the complete status information to the ARQ sender, i.e.,
the status message comprises information about the entire receive window.
Therefore the size of the status message increases with the number of
negative acknowledgement to be reported by the receiving protocol entity.
Due to varying radio channel quality or inappropriate resource
assignments the available radio resources may not be sufficient to
transmit an entire status message.

[0013] Examples of solutions to the problem that the available resources
are too small to send a full status message are to either prioritize
status messages to ensure that enough resources are available which
implies that other transmissions are delayed, or to postpone the
transmission of a status message until sufficient resources are available
which would lead to window stalling or increased transmission delays
which are also unfavourable. These solutions are likely to lead to
situations where the receiver may not be allowed to send any status
message due to insufficient radio resources.

SUMMARY

[0014] An object of the present invention is to provide a mechanism for
improving handling of a status message transmitted from a data unit
receiving node to a data unit sending node.

[0015] According to a first aspect of the present invention, the object is
achieved by a method in a receiving node, for handling status information
of data units transmitted from a sending node to the receiving node over
a radio link. The receiving node establishes that a number of data units
being transmitted by the sending node are missing. The receiving node
sends a reduced status message to the sending node over the radio link.
The message is reduced such that it comprises the negative
acknowledgement for a first part of missing data units and omits negative
acknowledgements for the rest of the missing data units. The omitted
negative acknowledgement for the rest of the missing data units will not
erroneously be interpreted as correctly received data units by the
sending node.

[0016] According to a second aspect of the present invention, the object
is achieved by a method in a sending node, for handling status
information of data transmitted from the sending node to the receiving
node over a radio link. The sending node transmits a stream of data units
over the radio link to the receiving node. The receiving node correctly
receives some of the transmitted data units but misses a number of the
transmitted data units. The sending node receives a reduced status
message from the receiving node over the radio link. The message is
reduced such that it comprises the negative acknowledgement for a first
part of missing data units and omits negative acknowledgement for the
rest of the missing data units. The omitted negative acknowledgement for
the rest of the missing data units will not erroneously be interpreted as
correctly received data units by the sending node.

[0017] According to a third aspect of the present invention, the object is
achieved by an arrangement in a receiving node for handling status
information of data units, transmitted from a sending node to the
receiving node over a radio link. The receiving node arrangement
comprises an establishing unit configured to establish that a number of
data units that has been transmitted by the sending node are missing and
a sending unit configured to send a reduced status message to the sending
node over the radio link. The message is reduced such that it comprises
the negative acknowledgement for a first part of missing data units and
omits negative acknowledgements for the rest of the missing data units.
The omitted negative acknowledgement for the rest of the missing data
units will not erroneously be interpreted as correctly received data
units by the sending node.

[0018] According to a fourth aspect of the present invention, the object
is achieved by an arrangement in a sending node, for handling status
information of data units, transmitted from the sending node to the
receiving node over a radio link. The sending node arrangement comprises
a sending unit configured to transmit a stream of data units over the
radio link to the receiving node. The receiving node correctly receives
some of the transmitted data units but misses a number of the transmitted
data units. The sending node arrangement further comprises a receiving
unit configured to receive a reduced status message from the receiving
node over the radio link. The message is reduced such that it comprises
the negative acknowledgement for a first part of missing data units and
omits negative acknowledgement for the rest of the missing data units.
The omitted negative acknowledgement for the rest of the missing data
units will not erroneously be interpreted as correctly received data
units by the sending node.

[0019] Since a reduced status report is used, comprising only the negative
acknowledgement for the first part of the sequence numbers of missing
data units but omitting negative acknowledgement for sequence numbers of
the rest of the missed number of data units, less resources are required
for the transmission which in turn implies that the handling of the
status report transmitted from the sending node to the receiving node is
improved.

[0020] Advantages of the present invention comprise that the receiving
node interprets the reduced status report correctly and does not advance
it's transmit window beyond any not successfully transmitted data units.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention is described in more detail with reference to
attached drawings illustrating exemplary embodiments of the invention and
in which:

[0022] FIG. 1 is a schematic block diagram illustrating a status message
according to prior art.

[0029] The invention is defined as a method and an arrangement which may
be put into practice in the embodiments described below.

[0030] FIG. 2 depicts a wireless telecommunication system 100, such as
e.g. E-UTRAN, LTE, WCDMA, EDGE, and WLAN. The wireless telecommunication
system comprises a sending node 110 and a receiving node 120. The sending
node 110 is adapted to transmit data units such as e.g. PDUs over a radio
link 130 to the receiving node 120. The sending node 110 may be a base
station such as a NodeB, an eNodeB or any other network unit capable to
transmit data units to a receiving node 120 over a radio link 130. The
receiving node 120 may be a wireless terminal such as a mobile phone, a
Personal Digital Assistant (PDA), a user equipment (UE) or any other
network node capable of receiving data units from a sending node over a
radio link 130. It may also be the opposite, so that the sending node 110
is a wireless terminal and the receiving node 120 is a base station.

[0031] To improve throughput, the sending node 110 and the receiving node
120 may use a window based Automatic Repeat request (ARQ) mechanism. In
this case the sending node 110 comprises a transmitting window and the
receiving node 120 comprises a receiving window. The window mechanism
allows the sending node 110 to continuously send data units while waiting
for acknowledgements. The window can be seen as a buffer.

[0032] The sending node 110 may be informed about the size of the
receiving window of the receiving node 120, to enable the sending node
110 to avoid sending more data units than the receiving node 120 can
concurrently handle. To do so, the sending node 110 may maintain a lower
window edge, holding the sequence number of oldest outstanding data unit
for which no positive acknowledgement has been received and an upper
window edge holding the sequence number of the next data unit to be
transmitted. It further ensures that the distance between the lower and
the upper window edge does not exceed the size of the receiver's window.
With this prerequisite the sending node 110 can send a whole sender
window of data units before receiving an acknowledgement of the first
data unit in the window while still ensuring lossless operation and
continuous data transmission. Upon reception of acknowledgements the
lower edge of the sender window is moved forward such that the first data
unit in the window is again the oldest transmitted but not yet
acknowledged data unit.

[0033] Similarly, the receiving node 120 may maintain a lower window edge
holding the sequence number of the oldest outstanding, i.e., next
expected data unit and an upper window edge holding the sequence number
following that of the highest received data unit. Both, the lower and the
upper window edge are advanced when a data unit with the corresponding
sequence number has been received. If the lower window edge equals the
upper window edge there are no outstanding data units. Otherwise, data
units may have been lost or at least re-ordered on lower layers and the
receiving node may send a status message towards the sending node 110.
Such a status message may comprise a list of sequence numbers of expected
but not yet received data units (at least the lower window edge and
potentially more) as well as the sequence number of the highest received
sequence number (upper window edge) or the sequence number following that
depending on the protocol specification.

[0034] The following describes some non-limiting and non-exclusive
examples how to handling status information of data units transmitted
from the sending node 110 to the receiving node 120.

[0035] Referring to FIG. 3, the sending node 110 transmits data units
(also referred to as Protocol Data Units, PDUs or packets) to the
receiving node 120. Before the transmission, each one of the data units
to be transmitted is associated with a sequence number 301 allowing the
receiving node 120 to detect re-ordering, to re-establish the data units
original order, to detect loss of data units and as a reference to be
used in status messages to be sent from the receiving node 120 to the
sending node 110.

[0036] The sending node 120 then transmits 302 a stream of data units over
the radio link 130 to the receiving node 120. In the example of FIG. 3,
data units with sequence numbers 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 are
transmitted to the receiving node 120. A data unit is represented by a
square containing the associated sequence number. In the example of FIG.
3, data units with sequence numbers 1, 5, 9 and 10 are correctly received
by the receiving node 120 as indicated by straight arrows. Data units
with sequence numbers 2, 3, 4, 6, 7 and 8 are not received or not
correctly received by the receiving node 120 as indicated by wavy arrows.

[0037] If the channel resources allow, the receiving node 120 will send a
complete status message to the sending node 110 (not shown in FIG. 3).
This complete status message may comprise a negative acknowledgement for
each one of the respective data units with sequence numbers 2, 3, 4, 6, 7
and 8, i.e., it contains e.g. a NACK_SN field for each missing data unit.
The complete status message may further comprise a cumulative positive
acknowledgement for the sequence numbers 1, 5, 9 and 10, e.g. an ACK_SN
field set to 11 indicating that this is the next expected sequence number
outside the receiving window.

[0038] When e.g. the channel quality is too poor for sending a complete
status message, as assumed in this example depicted in FIG. 3, the
receiving node 120 may send 304 a reduced status message to the sending
node 110 305, 306, to adapt the transmission to the available channel
resources over the radio link 130. According to one example, the
receiving node 120 includes in the reduced status message, only as many
negative acknowledgements as fit in because of the limited resources
while omitting the other negative acknowledgements. In this example the
reduced status message only contains three negative acknowledgements,
represented e.g. by three NACK_SN fields set to the sequence numbers 2, 3
and 4.

[0039] According to a state-of-the-art protocol, a cumulative positive
acknowledgement (e.g. ACK_SN) would indicate successful reception of all
data units with sequence numbers up to but excluding 11, and excluding
those data units for which an explicit negative acknowledgement is
contained. A state of the art sending node would consequently interpret
the reduced status message so as if the data units with sequence numbers
6, 7 and 8 have been successfully received. It would therefore not
perform retransmissions of those data units and may even discard the data
from its transmitting window so that no retransmission can be performed
later.

[0040] To overcome this problem of misunderstanding the cumulative
positive acknowledgement (e.g. ACK_SN) may be set differently for a
reduced status message compared to a complete status message. According
to a first embodiment the positive acknowledgement (e.g. ACK_SN) in a
reduced status message is set such that it does not acknowledge any data
units with sequence number equal to or larger than the sequence numbers
of data units that where omitted in the reduced status message. I.e. the
reduced status message comprises positive acknowledgements only for data
units with sequence number equal to or smaller than the lowest sequence
numbers that was omitted in the reduced status message.

[0041] In that way the sending node 110 will not erroneously interpret
that the data units missing in the receiving node's window but not
reported in said reduced status message as correctly received. In this
example this means that the reduced status message 305 shall only
positively acknowledge data units 1 and 5, but not data units 9 and 10,
According to one embodiment of this example, a method sets the ACK_SN
field in the reduced status message to 6 thereby indicating to the
sending node 110 the successful reception of all data units up to but not
including sequence number 6 and explicitly excluding sequence numbers 2,
3 and 4. This implies that the sending node 110 receiving 306 the reduced
status message will treat it like any complete status message and make
the correct status interpretation, i.e., regard the data units with
sequence number 1 and 5 as correctly received and retransmit data units
with sequence numbers 2, 3 and 4. The sending node 110 does not need to
know that the status message is a reduced status message. It however
expects further status messages providing information about the other
outstanding data units with sequence numbers 6, 7, 8 9, and 10. As a
benefit of this embodiment there is no need for any indicator indicating
that the status message is a reduced status message, i.e. that it does
not contain negative acknowledgements (e.g. NACK_SNs) for all missing
(non-received) data units or segments thereof but only for a sub-set.

[0042] In this embodiment it may be preferable not to send another status
message before the receiving node 120 is sure that the status message has
been received, e.g. after receiving an expected retransmission. To avoid
sending another status message, a status prohibit timer may be applied
which may be started upon transmission of a data unit and which prevents
the receiving node from sending a status message while running.

[0043] According to a second embodiment a special identifier comprised in
the status message is used to indicate that this is a reduced status
message and not a full status message. For example the reduced status
message may negatively acknowledge data units (e.g. by means of one or
more NACK_SN fields) triggering retransmissions from the sending node 110
to the receiving node 120. However, said identifier may prevent the
sending node 110 from interpreting any not explicitly negatively
acknowledged data units as successfully acknowledged. This means in
particular that the sending node 110 is not allowed to advance the lower
edge of its receiving window and from discarding any associated data
units. In the example above (not shown) a first reduced status message
may contain negative acknowledgements for data units 6, 7 and 8 without
being interpreted as a positive (cumulative) acknowledgement for the data
units with sequence numbers 1, 2, 3, 4, 5, 9 and 10.

[0044] A suitable field to indicate the special format may be the CPT
field in e.g. the currently defined status format according to E-UTRAN. A
special code point may be defined to indicate such special NACK message.

[0045] Several reduced status messages may be sent if the sending node 110
operates according to this embodiment without causing any harm to the
transmission window state even if status messages are re-ordered or lost.

[0046] If it is known that the field of acknowledgement (e.g. ACK_SN)
should not be interpreted at the sending node 110, it may even be
omitted, i.e. a special status message format is used for this purpose
which optimizes the size of the status message and would allow
transmitting further negative acknowledgements in the given radio
resources.

[0047] Alternatively, in this particular example the cumulative positive
acknowledgement may be set to the upper edge of the receiving window
(ACK_SN=11 in this example) indicating to the sending node that at least
(a segment of) the data unit with sequence number 10 has been received.

[0048] Often a status message is requested by the sending node 110 using a
poll flag included in a data unit. This is typically done in order to
advance the sender window. In that case a status message according to the
second embodiment comprising only negative acknowledgement but preventing
the sending node 110 from advancing its transmission window does not
help.

[0049] According to a third embodiment, a special identifier comprised in
the status message is used to indicate that this is a reduced status
message and not a full status message. Upon reception of this status
message the sending node 110 may advance the lower edge of the
transmission window up to the lowest negatively acknowledged data unit.
It may however not advance it beyond the highest negatively acknowledged
sequence number unless it receives another status message allowing it to
do so.

[0050] Special means such as a status prohibit timer in the receiving node
120 must ensure that the receiving node 120 sends only one reduced status
messages comprising only a sub-set of the negative acknowledgements.

[0051] In the example above (not shown in the figure) the reduced status
message would in addition to the special identifier contain negative
acknowledgement for the data units with sequence numbers 2, 3 and 4. The
sending node 110 can move the lower edge of the window up sequence number
2, i.e., remove the data unit with sequence number 1 from the
transmission window.

[0052] According to a fourth embodiment, if several reduced status
messages are needed to report all missing data units, a special status
message type may be defined for the first reduced status message
comprising negative acknowledgement closest to the lower window edge and
a second special status message type may be defined for the following
reduced status messages comprising any other negative acknowledgements.

[0053] Only a reduced status message of the first special status message
format allows the sending node 110 to advance the lower window edge up to
the first negatively acknowledged sequence number whereas the reduced
status message of the second special status message format must not be
used to advance the transmission window.

[0054] In this embodiment the cumulative positive acknowledgement field is
not needed and may be removed from the special status message formats in
order to save transmission resources.

[0055] In the example above (not shown in the figure) the first reduced
status message would comprise negative acknowledgements for the data
units with sequence numbers 2, 3 and 4. A reduced status message of the
second special status message format comprises negative acknowledgements
for the data units with sequence numbers 6, 7 and 8.

[0056] The method steps in the receiving node 120 for handling status
information of data units or data unit segments "data units" transmitted
from the sending node 110 to the receiving node 120 over a radio link 130
according to some embodiments will now be described with reference to a
flowchart depicted in FIG. 4. The method comprising the steps of:

[0057]
401. The receiving node 120 establishes that a number of data units 2, 3,
4, 6, 7, 8 that has been transmitted by the sending node 110 are missing.

[0058] 402. The receiving node 120 sends a reduced status message to the
sending node 120 over the radio link. The message is reduced such that it
comprises the negative acknowledgement for a first part 2, 3, 4 of
missing data units and omits negative acknowledgements for the rest 6, 7,
8 of the missing data units. The omitted negative acknowledgement for the
rest 6, 7, 8 of the missing data units will not erroneously be
interpreted as correctly received data units by the sending node 110.

[0059] In some embodiments the negative acknowledgement for the first
part 2, 3, 4 of missing data units comprised in the reduced status
message is represented by as many negative acknowledgements as fitted in
the reduced status message because of limited resources.

[0060] The
receiving node 120 may use a receiving window. In some embodiments the
negative acknowledgement for the first part 2, 3, 4 of the missing data
units, are the missing data units which are closest to a lower edge of
the receiving window.

[0061] In some embodiments the reduced status
message positively acknowledges data units up to but not including the
first missing data unit for which a negative acknowledgement was omitted
in the reduced status message.

[0062] In one embodiment, the positively
acknowledgement is performed by setting an ACK_SN field to the first
missing data unit for which a negative acknowledgement was omitted in the
reduced status message, meaning that data units with sequence numbers up
to but not including the first missing data unit for which a negative
acknowledgement was omitted, are acknowledged.

[0063] In some embodiments
the reduced status message comprises an indication that no correctly
received data units 1, 5,9,10 will be acknowledged in the reduced status
message such that only negative acknowledged data units will be triggered
to be retransmitted by the sending node 110. A special format of the
reduced status message may be the indication that no correctly received
data units 1, 5,9,10 will be acknowledged in the reduced status message.
In some embodiments the field of acknowledgement in the reduced status
message is not used for acknowledgement, but is instead used for a
further negative acknowledgement.

[0064] 403. This is an optional step.
In some embodiments a first special status message type is used for the
reduced status message comprising the negative acknowledgement for the
first part 2, 3, 4 of missing data units closest to a lower edge of the
receiving window. In this step the receiving node 120 may send a second
reduced status message to the sending node 120 over the radio link 130
using a second special status message type. The second reduced status
message comprises at least one of the omitted negative acknowledgements
for the rest 6, 7, 8 of the missing data units.

[0065] To perform the method steps above for handling status information
of data units or data unit segments "data units" transmitted from the
sending node 110 to the receiving node 120 over the radio link 130, the
receiving node 120 comprises an arrangement 500 depicted in FIG. 5.

[0066] The receiving node arrangement 500 comprises an establishing unit
510 configured to establish that a number of data units 2, 3, 4,6,7,8
that has been transmitted by the sending node (110) are missing.

[0067] The receiving node arrangement 500 further comprises a sending unit
520 configured to send a reduced status message to the sending node 120
over the radio link. The message is reduced such that it comprises the
negative acknowledgement for a first part 2, 3, 4 of missing data units
and omits negative acknowledgements for the rest 6, 7, 8 of the missing
data units. The omitted negative acknowledgement for the rest 6, 7, 8 of
the missing data units will not erroneously be interpreted as correctly
received data units by the sending node 110.

[0068] The negative acknowledgement for the first part 2, 3, 4 of missing
data units comprised in the reduced status message may be represented by
as many negative acknowledgements as fitted in the reduced status message
because of limited resources.

[0069] The receiving node 120 may use a receiving window and in some
embodiments the negative acknowledgement for the first part 2, 3, 4 of
the missing data units, are the missing data units which are closest to a
lower edge of the receiving window.

[0070] A first special status message type may be arranged to be used for
the reduced status message comprising the negative acknowledgement for
the first part 2, 3, 4 of missing data units closest to a lower edge of
the receiving window. The sending unit 520 may further be configured to
send a second reduced status message to the sending node 120 over the
radio link 130 using a second special status message type. The second
reduced status message is arranged to comprise at least one of the
omitted negative acknowledgements for the rest (6, 7, and 8) of the
missing data units.

[0071] In some embodiments the reduced status message is arranged to
positively acknowledge data units up to but not including the first
missing data unit for which a negative acknowledgement was omitted in the
reduced status message.

[0072] In one embodiment the positively acknowledgement is arranged to be
performed by setting a ACK_SN field to the first missing data unit for
which a negative acknowledgement was omitted in the reduced status
message, meaning that data units with sequence numbers up to but not
including the first missing data unit for which a negative
acknowledgement was omitted, are acknowledged.

[0073] In some embodiments the reduced status message is arranged to
comprise an indication that no correctly received data units 1, 5,9,10
will be acknowledged in the reduced status message such that only
negative acknowledged data units will be triggered to be retransmitted by
the sending node 110. A special format of the reduced status message may
be the indication that no correctly received data units 1, 5,9,10 will be
acknowledged in the reduced status message.

[0074] In some embodiments, the field of acknowledgement in the reduced
status message is not used for acknowledgement, but is instead arranged
to be used for a further negative acknowledgement.

[0075] The method steps in the sending node 110, for handling status
information of data units or data unit segments "data units" transmitted
from the sending node 110 to the receiving node 120 over the radio link
130, according to some embodiments will now be described with reference
to a flowchart depicted in FIG. 6. The method comprises the steps of:

[0076] 601. The sending node 110 transmits a stream of data units or data
unit segments 1, 2,3,4,5,6,7,8,9,10, over the radio link 130 to the
receiving node 120. The receiving node 120 correctly receives some of the
transmitted data units 1, 5,9,10 but misses a number of the transmitted
data units 2, 3, 4,6,7,8.

[0077] 602. The sending node 110 then receives
a reduced status message from the receiving node 120 over the radio link
130. The message is reduced such that it comprises the negative
acknowledgement for a first part 2, 3, 4 of missing data units and omits
negative acknowledgement for the rest 6, 7, 8 of the missing data units.
The omitted negative acknowledgement for the rest 6, 7, 8 of the missing
data units will not erroneously be interpreted as correctly received data
units by the sending node 110.

[0078] In some embodiments, the negative
acknowledgement for the first part 2, 3, 4 of missing data units
comprised in the reduced status message is represented by as many
negative acknowledgements as fitted in the reduced status message because
of limited resources.

[0079] In some embodiments the negative
acknowledgement for the first part 2, 3, 4 of missing data units are the
missing data units which are closest to a lower edge of a receiving
window in the receiving node 120.

[0080] In some embodiments the reduced
status message positively acknowledges data units up to but not including
the data unit for which a negative acknowledgement was omitted in the
reduced status message.

[0081] In one embodiment, the positively
acknowledgement is performed by setting an ACK_SN field to the first
missing data unit for which a negative acknowledgement was omitted in the
reduced status message. This means that data units with sequence numbers
up to but not including the first missing data unit, for which a negative
acknowledgement was omitted, are acknowledged.

[0082] The reduced status
message may comprise an indication that no correctly received data units
1, 5, 9, 10 will be acknowledged in the reduced status message such that
only negative acknowledged data units will be triggered to be
retransmitted. A special format of the reduced status message may be the
indication that no correctly received data units 1, 5,9,10 will be
acknowledged in the reduced status message.

[0083] In some embodiments,
the field of acknowledgement in the reduced status message is not used
for acknowledgement, but is instead used for a further negative
acknowledgement.

[0084] 603. This is an optional step. In some
embodiments the sending node 110 uses a transmission window. In this step
the sending node 110 moves a lower edge of the transmission window up to
the lowest negatively acknowledged data unit.

[0085] 604. This is also an
optional step. In some embodiments a first special status message type is
used for the reduced status message comprising the negative
acknowledgement for the first part 2, 3, 4 of missing data units closest
to a lower edge of the receiving window of the receiving node 120. In
this step the sending node receives a second reduced status message from
the receiving node 120 over the radio link 130, wherein a second special
status message type is used. The second reduced status message comprises
at least one of the omitted negative acknowledgements for the rest 6, 7,
8 of the missing data units.

[0086] In some embodiments, reception of
the reduced status message of the first special status message type
allows the sending node 110 to advance the lower transmission window edge
up to the first negatively acknowledged sequence number whereas the
reduced status message of the second special status message type does not
allow advancing the transmission window.

[0087] To perform the method steps above for handling status information
of data units or data unit segments "data units" transmitted from the
sending node 110 to the receiving node 120 over a radio link 130, the
sending node 110 comprises an arrangement 700 depicted in FIG. 7.

[0088] The sending node arrangement 700 comprises a sending unit 710
configured to transmit a stream of data units 1, 2,3,4,5,6,7,8,9,10, over
the radio link 130 to the receiving node 120. The receiving node 120
correctly receives some of the transmitted data units 1, 5,9,10 but
misses a number of the transmitted data units 2, 3, 4,6,7,8.

[0089] The sending node arrangement 700 further comprises a receiving unit
720 configured to receive a reduced status message from the receiving
node 120 over the radio link 130. The which message is reduced such that
it comprises the negative acknowledgement for a first part 2,3,4 of
missing data units and omits negative acknowledgement for the rest 6,7,8
of the missing data units. The omitted negative acknowledgement for the
rest 6, 7, 8 of the missing data units will not erroneously be
interpreted as correctly received data units by the sending node 110.

[0090] In some embodiments the negative acknowledgement for the first part
2, 3, 4 of missing data units comprised in the reduced status message is
represented by as many negative acknowledgements as fitted in the reduced
status message because of limited resources. The negative acknowledgement
for the first part 2, 3, 4 of missing data units may be the missing data
units which are closest to a lower edge of a receiving window in the
receiving node 120. Note that sequence numbers may wrap around at some
point in time so that "lower" is not relevant any longer. In this
document the "lowest sequence number" refers to the sequence number that
is closest to the lower window edge. Further, all comparisons may be done
modulo to some reference sequence number.

[0091] According to some embodiments a first special status message type
is used for the reduced status message comprising the negative
acknowledgement for the first part 2, 3, 4 of missing data units closest
to a lower edge of the receiving window.

[0092] The receiving unit 720 may further be configured to receive a
second reduced status message from the receiving node 120 over the radio
link, wherein a second special status message type is used, and the
second reduced status message comprising at least one of the omitted
negative acknowledgements for the rest 6, 7, 8 of the missing data units.

[0093] In some embodiments the reception of the reduced status message of
the first special status message type allows the sending node 110 to
advance the lower window edge up to the first negatively acknowledged
sequence number whereas the reduced status message of the second special
status message type does not allow advancing the transmission window.

[0094] In some embodiments the reduced status message positively
acknowledges data units up to but not including the data unit for which a
negative acknowledgement was omitted in the reduced status message.

[0095] In one embodiment the positively acknowledgement is performed by
setting an ACK_SN field to the first missing data unit for which a
negative acknowledgement was omitted in the reduced status message. This
means that data units with sequence numbers up to but not including the
first missing data unit, for which a negative acknowledgement was
omitted, are acknowledged.

[0096] The reduced status message may comprise an indication that no
correctly received data units 1, 5,9,10 will be acknowledged in the
reduced status message such that only negative acknowledged data units
will be triggered to be retransmitted.

[0097] A special format of the reduced status message may be the
indication that no correctly received data units 1, 5,9,10 will be
acknowledged in the reduced status message.

[0098] In some embodiments the field of acknowledgement in the reduced
status message is not used for acknowledgement, but is instead used for a
further negative acknowledgement.

[0099] The sending node 110 may use a transmission window. In some
embodiments the sending node arrangement 700 further comprises a window
managing unit 730 configured to move a lower edge of the transmission
window up to the lowest negatively acknowledged data unit.

[0100] The present mechanism for handling status information of data units
transmitted from the sending node 110 to the receiving node 120 over a
radio link 130, may be implemented through one or more processors, such
as a processor 530 in the sending node arrangement 500 depicted in FIG. 5
or the processor 740 in the receiving node apparatus 700 depicted in FIG.
7, together with computer program code for performing the functions of
the present solution. The program code mentioned above may also be
provided as a computer program product, for instance in the form of a
data carrier carrying computer program code for performing the present
solution when being loaded into the sending node 110 or the receiving
node 120. One such carrier may be in the form of a CD ROM disc. It is
however feasible with other data carriers such as a memory stick. The
computer program code can furthermore be provided as pure program code on
a server and downloaded to the sending node 110 or the receiving node 120
remotely.

[0101] Some examples of the present method may be described as a method a
sending node 110 for handling status information of data units
transmitted from the sending node 110 to the receiving node 120 over a
radio link 130.

[0102] The method comprises the step of transmitting a stream of data
units or data unit segments over the radio link to the receiving node
120, each data unit being associated with a sequence number. The method
comprises the further step of receiving a reduced status message from the
receiving node 120. The reduced status message comprises information and
an indication that the reduced status massage is reduced and therefore
shall not be interpreted as a complete status message.

[0103] In some examples, the reduced status message further comprises an
indication how to interpret fields in the reduced status message
comprising the information.

[0104] The information not being complete, relates to which of the data
units and their respective sequence number of the transmitted stream of
data units that are received, i.e. acknowledged by the receiving node,
and which are not received, i.e. not acknowledged by the receiving node.

[0105] Some further examples of the present method may be described as a
method in a receiving node 120 for handling status information of data
units transmitted from a sending node 110 to the receiving node 120 over
a radio link 130.

[0106] The method comprises the step of receiving a stream of data units
or data unit segments over the radio link from the sending node, each
data unit being associated with a sequence number. The method further
comprises the step of sending a reduced status message to the sending
node. In the reduced status message the acknowledge of a sequence number
associated with a data unit, e.g. the ACK_SN, is set such that it does
not acknowledge any data units with a respective associated sequence
number equal to or larger than the not acknowledge of a sequence number
associated with a data unit, e.g. NACK_SNs that is omitted in the reduced
status message.

[0107] When using the word "comprise" or "comprising" it shall be
interpreted as non-limiting, i.e. meaning "consist at least of".

[0108] The present invention is not limited to the above described
preferred embodiments. Various alternatives, modifications and
equivalents may be used. Therefore, the above embodiments should not be
taken as limiting the scope of the invention, which is defined by the
appending claims.